1. Field of the Invention
The present invention relates to a toner for the use in developing latent images and a method of manufacturing thereof, a two-component developer, a developing device and an image forming apparatus, in an image forming apparatus of an electrophotographic system, an electrostatic printing system or the like.
2. Description of the Related Art
Toners for visualizing latent images are used in various image forming processes and one example thereof is use in an electrophotographic image forming process. Image forming apparatuses employing the electrophotographic image forming process generally perform a charging step of uniformly charging a photosensitive layer on the surface of a photoreceptor drum serving as an image bearing member; an exposure step of projecting signal light corresponding to an original image on the surface of the photoreceptor drum that is being charged to form an electrostatic latent image; a development step of visualizing the electrostatic latent image on the surface of the photoreceptor drum by supplying electrophotographic toner thereto; a transfer step of transferring a toner image formed on the photoreceptor drum to a recording medium such as paper and OHP sheets; a fixing step of fixing the toner image onto the recording medium under heat, pressure and the like; and a cleaning step of eliminating toner and the like remaining on the surface of the photoreceptor drum after the toner image is transferred, with a cleaning blade and for cleaning the surface of the photoreceptor drum, to subsequently form a desired image on the recording medium. Transfer of a toner image onto a recording medium may be performed through an intermediate transfer medium.
The electrophotographic toner is obtained in a manner that toner material including a binder resin and a colorant as main components, to which a release agent, a charge control agent and the like are added when necessary, and are mixed, melt-kneaded, cooled and solidified, then subjected to a knead-pulverization method for pulverization and classification or to a polymerization method represented by a suspension polymerization method, an emulsification polymerization method and the like.
In recent years, various efforts have been made in various fields from a viewpoint of global environmental protection, one of which is to decrease environmental load by reducing waste products. Today, a number of raw materials are manufactured from oil and reducing heat quantity necessary for manufacturing such raw materials and burning the waste products thereof and carbon dioxide generated accordingly, is important from the viewpoint of suppression of global warming. On the other hand, carbon dioxide generated by burning plants that took in carbon dioxide from the atmosphere through photosynthesis does not change the total amount of carbon dioxide in the atmosphere, because the carbon dioxide that the plants took in was originally present in the atmosphere. This is so-called carbon neutral and since a plant-derived material is carbon-neutral and use thereof is able to fix the carbon dioxide amount in the atmosphere, leading to suppression of global warming, much attention has been focused thereon.
Furthermore, for the problem of depletion of fossil fuels including oil, efforts have been made to use resources derived from natural products that are non-oil resources, and the plant-derived material particularly attracts attention.
The plant-derived material is generally called a biomass, and a plastic made from biomass is called by various terms, such as a biomass polymer, a biomass plastic, or an oil-free polymer material. Among the biomass, lignin is a natural polymer present in trees and is obtainable from wood or wood-based waste products, and from a viewpoint of improving the global environment and an effective use of resources and the like, attention has been focused thereon in recent years.
Also in the electrophotographic field, efforts have been made to take into consideration the global environment, specifically environmental safety, reduction of waste products, energy saving and the like and use of biodegradable resins using biomass or the like is proposed.
Japanese Unexamined Patent Publication JP-A 5-216271 (1993) discloses electrophotographic toner that contains, with consideration for global environmental protection, resins obtained by esterifying or etherifying lignin and cellulose as components constituting the binder resin in the toner, and still has a sufficient anti-offset property and a low-temperature fixing property in fixing and causes no entanglement to a fixing roller.
For fixing a toner image transferred on the recording medium such as paper and OHP sheets, a contact heat fixing method represented by a heating roller and the like is often used and the fixing property of toner to the recording medium in this method is able to be indicated by an extent of a fixing non-offset range that is a temperature range capable of fixing between a minimum fixing temperature at which a low-temperature offset does not appear and a temperature at which a high-temperature offset starts to appear.
To improve the fixing property of toner to the recoding medium, that is, to obtain a toner having a wide fixing non-offset range, use of a resin having a cross-linked structure as the binder resin contained in the toner and use of a resin including high-molecular-weight substances and low-molecular-weight substances are proposed. However, when a ratio of the cross-linked components in the binder resin or the high-molecular-weight substances is increased to improve the anti-high-temperature offset property of the toner, melt viscosity of the binder resin is increased to make the low-temperature fixing property of the toner insufficient. Therefore, to obtain a toner having a wide fixing non-offset range, it is important that blending balance and physical properties of the resin components in the binder resin are controlled.
In the technology disclosed in JP-A 5-216271, the content rate of the resin obtained by esterifying or etherifying lignin and cellulose as components constituting the binder resin, and another component of the binder resin are unclear, therefore it is not said that the blending balance and physical properties of the resin components in the binder resin are controlled, as a result, there is a case that the toner has a narrow fixing non-offset range to deteriorate the fixing property.